27 May 2009

Can fig wasps bluff their way to mating success?

“Not so tough now, are ya?”

I think everyone secretly hopes to utter that phrase someday to someone who blusters and bullies and threatens.

There’s a scene in Quentin Tarantino’s film Death Proof where Kurt Russell’s character, Stuntman Mike – who has just been terrorizing a group of women on the highway – gets shot. He runs like hell and is pretty soon all but balling his eyes out.

I like the scene a lot, because we rarely see it acknowledged in movies or TV that getting shot hurts.

In animal behaviour research, there’s been a lot of interest in animals that bluff. Bluffing is an example of a dishonest signal: looking strong when you’re really not. It’s interesting because theory says it’s possible to have these dishonest signals, but it’s tricky. They will only stay in the population only under certain circumstances. For instance, not every confrontation can escalate to a fight. Richard Dawkins presents some of these theoretical “hawk versus dove” models in chapter 5 of The Selfish Gene.

In this paper, Moore and colleagues present evidence for bluffing in fig wasps. The males have two morphs, typical and atypical. The atypical males are, well, not typical: they make up about 18% of the males. These males have longer jaws (mandibles, if you want the $5 word) for their head size, and they also tend to have larger heads.

The questions are:

When do male wasps fight? When there are lots of other males with mandibles about the same size. This supports the idea that wasps won’t fight if there is a big mismatch in jaws, consistent with them evaluating their opponents.

Who wins fights? The male with the bigger mandibles wins about two-thirds of matches, except...

Which morph fight better? Atypical males are less likely to win fights and appeared more likely to sustain injury.

Who gets to mate? The atypical males get 44% of matings when they make up less than 20% of the males &ndash more than their fair share.

There are a few caveats with this paper. First, the authors themselves admit the sample sizes are pretty small. They only observed 18 matings, for example, and only 10 of those were by animals they observed fighting.

Another qualifier is that there several inferences; reasonable ones, but inferences nevertheless. For instance, they infer that male wasps evaluate mandible size, and that they will retreat if outmatched. Since these were all spontaneously occurring fights in the figs the wasps inhabit, they have not done any experimental pairings to test that.

In the long term, it would be interesting to see if people can get enough data to see if the atypical males’ apparent bluffing, and the costs (getting beat up) and benefits (sex!) are in line with the theoretical predictions of game theory.